Tire recycling is a relatively new industry that began in 1985 to reduce the large number of tires stored in tire dumps and to reduce the number of tires going to landfill. The efforts in the 1990's were successful in both reducing the number of tires in dumps and recycling about 80% of the roughly 300 million tires that are now scrapped each year. As the production of recycled rubber has grown, so have the uses for recycled tire products. Currently, a majority of the recycled tires are used for tire derived fuel, civil engineering applications and production of ground rubber.
A tire is constructed of rubber and reinforcing materials including steel, reinforcing fiber such as polyester, and other materials. A new passenger tire weighs approximately 20 pounds and is composed, by weight, of about 70% rubber, 15% steel and 15% other material such as re-enforcing fiber.
Currently, tire recycling operations occur in three-stages: (1) collection and transportation of spent tires to a processing site, (2) shredding the tires into chips, and (3) processing the chips into various marketable products. Since a tire occupies such a large volume, its transportation cost is quite high, limiting the practical distance between a collection and a processing site to about 150 miles. Process economics dictate that plants must be sized to recycle at least two million tires per year. But such sized plants place a high demand on available tires and inevitably require that tires be shipped from ever more distant sources. Furthermore, the plants consume a large amount of energy and have high maintenance costs. As a result, these current operations tend to provide recycling companies with only a marginal return on their investment.
There are several patents that describe other methods of reclaiming the rubber from tires. Some of these involve the use of high pressure fluids such as the patents by Rutherford (U.S. Pat. No. 5,794,861) and Shinal (U.S. Pat. No. 5,683,038). In Veres (U.S. Pat. No. 5,482,215) a tread strip is fed in a flat state past a rotary cutter removing the tread rubber in a particulate form and the remaining belt is processed with ultra high pressure fluids. Bedjukh et al. (U.S. Pat. No. 6,391,930) describes a method for destroying tires with metallic cords using electric discharge.
There are other patents that refer to the use of tire pre-softening agents including a patent by Hunt, et al. (U.S. Pat. No. 5,362,759 and U.S. Pat. No. 5,611,462), Hunt and Hall (U.S. Pat. No. 5,362,759), Wortham (U.S. Pat. No. 6,872,754), Adkins (U.S. Pat. No. 5,905,095), Dobozy (U.S. Pat. No. 5,316,224), and Martinez (U.S. Pat. No. 5,304 . . . ). All of these patents, with the exception of the Martinez patent use shredded tires as the basic feedstock and reduce the size of the rubber by grinding the softened chips with the wire in place. The Martinez patent soaks primarily whole tires and then separates the tire components in a “pulverizing tank” using fluid or mechanical force. The first set of patents, while using less energy due to the pre-softened rubber, still use more energy and require more maintenance than necessary because the steel is still imbedded in the rubber during the grinding process. The Martinez patent avoids grinding the rubber with the metal embedded but introduces other problems associated with handling and soaking whole tires.
All the patents cited above use various chemicals to pre-soften the tires including d-limonene, a d-limonene/DMSO mixture, a wide range of organic solvents such as benzene, toluene, xylene, tetrahydronaphthalene and many others, as well as a 700 degrees Fahrenheit mixture of isocyanides, latex, polyurethane, soybean oil.